Summary form only given.It has previously been shown that a traveling-wave optical parametric amplifier can generate multimode squeezed states of light. Homodyne detection of multimode squeezed light, under certain physical conditions, results in sub-Poissonian statistics of photons not only in time but also in the transverse plane of the light beam. Of particular relevance to applications is a situation when the cross section of the light beam contains several nonoverlapping areas with sub-Poissonian statistics of photons within each of them. Under photodetection of such a beam of light, several sub-shot-noise photocurrents can be produced according to the number of independent areas with sub-Poissonian statistics. This is in drastic contrast to the case of a single-mode sub-Poissonian light beam, where any attempt to collect light only from a part of the beam deteriorates the degree of shot-noise reduction. This property of multimode squeezed light opens a range of new interesting applications in optical imaging, optical parallel processing of information, parallel computing, and many other phenomena where it is desirable to have the regular statistics of photons across the transverse plane of the electromagnetic wave. We describe the application of multimode squeezed light in sub-shot-noise microscopy, noiseless amplifications of optical images, and optical imaging. We also consider the possibility of improving the resolution in optical imaging and microscopy beyond the Rayleigh limit via multimode squeezed light.
Label-free optical microscopy through absorption or scattering spectroscopy provides fundamental insights across biology and materials science, yet its sensitivity remains fundamentally limited by photon shot noise. While recent demonstrations of quantum nonlinear microscopy show sub-shot-limited sensitivity, they are intrinsically limited by availability of high peak-power squeezed light sources. Here, we introduce squeezing-enhanced photothermal (SEPT) microscopy, a quantum imaging technique that leverages twin-beam quantum correlations to detect absorption induced signals with unprecedented sensitivity. SEPT achieves 3.5 dB noise suppression beyond the standard quantum limit, enabling a 2.5-fold increase in imaging throughput or 31% reduction in pump power, while providing an unmatched versatility through the intrinsic compatibility between continuous-wave squeezing and photothermal modulation. We showcase SEPT applications by providing high-precision characterization of nanoparticles and revealing subcellular structures, such as cytochrome c, that remain undetectable under shot-noise-limited imaging. By combining label-free contrast, quantum-enhanced sensitivity, and compatibility with existing microscopy platforms, SEPT establishes a new paradigm for molecular absorption imaging with far-reaching implications in cellular biology, nanoscience, and materials characterization.